A sensor for testing biomarkers in nano litre volumes of plasma based on luminescence

Abstract

A sensor for sensing photons in liquids comprises: a microfluidic substrate comprising a blood inlet, a buffer inlet, a mixing region configured to mix blood with buffer to provide a sample, and a plurality of microfluidic detection chambers each configured to receive a volume of analyte of less than 5 micro litres, wherein the microfluidic substrate is nontransparent and has a planar face. The sensor also comprises a semiconductor substrate comprising a plurality of single photon avalanche photodiodes facing the planar face of the microfluidic substrate and arranged in a plurality of primary arrays of photodiodes and at least one secondary array of photodiodes. The sensor also comprises a plurality of sensing channels, wherein each sensing channel of the plurality of sensing channels comprises one of the microfluidic detection chambers and a corresponding one of the primary arrays of photodiodes. Each one of the photodiodes in the secondary array of photodiodes is covered to prevent ingress of light and a secondary charge count derived from the secondary array of photodiodes is indicative of a dark count. An adjusted charge count is provided by using the dark count value to adjust the primary charge count.

1 . A sensor for sensing photons in liquids, the sensor comprising:
 a microfluidic substrate comprising a blood inlet, a buffer inlet, a mixing region configured to mix blood with buffer to provide a sample, and a plurality of microfluidic detection chambers each configured to receive a volume of analyte of less than 5 micro litres, wherein the microfluidic substrate is non-transparent such as to prevent photons from passing through the microfluidic substrate, wherein the microfluidic substrate comprises a planar face and each microfluidic detection chamber comprises a transparent aperture located in the planar face;   a semiconductor substrate comprising a plurality of single photon avalanche photodiodes facing the planar face of the microfluidic substrate and arranged in a plurality of primary arrays of photodiodes and at least one secondary array of photodiodes,   a plurality of sensing channels, wherein each sensing channel of the plurality of sensing channels comprises one of the microfluidic detection chambers and a corresponding one of the primary arrays of photodiodes arranged such that each photodiode in the primary array is aligned with and no more than 1,000 micrometres from its corresponding microfluidic detection chamber so as to receive photons emitted within the corresponding microfluidic detection chamber, wherein a primary charge count derived from the primary array of photodiodes provides a pre-adjusted value of photon count indicative of a total number of photons emitted within the corresponding microfluidic detection chamber;   wherein each one of the photodiodes in the secondary array of photodiodes is covered to prevent ingress of light and wherein a secondary charge count derived from the secondary array of photodiodes is indicative of a dark count;   wherein an adjusted charge count is provided by using the dark count value to adjust the primary charge count.   
     
     
         2 .- 50 . (canceled) 
     
     
         51 . The sensor of  claim 1 , wherein the non-transparent microfluidic substrate has an optical density attenuation coefficient of at least 1,00, preferably at least 1,000. 
     
     
         52 . The sensor of  claim 1 , wherein the microfluidic substrate further comprises a blood filter configured to receive blood from the blood inlet and to release blood plasma for mixing with buffer to provide a sample. 
     
     
         53 . The sensor of  claim 1 , further comprising: a temperature sensor circuit comprising: a temperature sensor; a heating element; and a heat sink element for use in regulating a temperature of the material being sensed wherein optionally:
 the temperature sensor circuit is one of a plurality of temperature sensor circuits and further optionally wherein each temperature sensor circuit of the plurality of temperature sensor circuits is located proximate to one or more primary arrays.   
     
     
         54 . The sensor of  claim 53 , wherein each temperature sensor circuit of the plurality of temperature sensor circuits is located between a pair of adjacent primary arrays wherein optionally:
 there is a one to one correspondence between each pair of primary arrays and each temperature sensor circuits such that there is a two to one correspondence between primary arrays and temperature sensor circuits.   
     
     
         55 . The sensor of  claim 53 , wherein each temperature sensor circuit is configured to maintain a target temperature based on a difference between the target temperature and a value for measured temperature obtained from the temperature sensor, wherein optionally the target temperature is between 36° C. and 38° C., preferably 37° C. 
     
     
         56 . The sensor of  claim 1 , wherein there is a one to one correspondence between each primary array of photodiodes and each secondary array of photodiodes. 
     
     
         57 . The sensor of  claim 53 , wherein the temperature sensor circuit is configured to generate thermal energy in the heating element. 
     
     
         58 . The sensor of  claim 1 , wherein the microfluidic substrate comprises an anti-fouling coating. 
     
     
         59 . The sensor of  claim 1 , wherein:
 each primary array of photodiodes comprises a grid of 64 single photon avalanche photodiodes; and/or   each secondary array of photodiodes comprises a grid of 16 single photon avalanche photodiodes; and/or   the plurality of primary arrays of photodiodes comprises 8 primary arrays and optionally the plurality of secondary arrays of photodiodes comprises 8 secondary arrays.   
     
     
         60 . The sensor of  claim 1 , wherein the semiconductor substrate is mounted on a face of a printed circuit board, and wherein the printed circuit board is a single planar printed circuit board. 
     
     
         61 . The sensor of  claim 1 , wherein the microfluidic substrate further comprises a blood filter configured to receive blood from the blood inlet and to release blood plasma for mixing with buffer to provide a sample and wherein the plurality of primary arrays of photodiodes comprises 8 primary arrays, wherein the temperature sensor, the heating element and the heat sink element are mounted on the printed circuit board. 
     
     
         62 . The sensor of  claim 1 , wherein the semiconductor substrate is one of a pair of corresponding semiconductor substrates. 
     
     
         63 . The sensor of  claim 60 , wherein the printed circuit board and the microfluidic substrate comprise corresponding alignment features for assisting alignment between each microfluidic detection chamber and its corresponding primary array of photodiodes. 
     
     
         64 . The sensor of  claim 1 , wherein each one of the single photon avalanche photodiodes is configured to detect wavelengths within the visible spectrum. 
     
     
         65 . The sensor of  claim 1 , wherein each one of the single photon avalanche photodiodes has a response time of less than 10 nanoseconds, preferably less than 1 nanosecond, more preferably less than 100 picoseconds; and/or
 wherein each one of the single photon avalanche photodiodes has a dynamic range of at least four orders of magnitude.   
     
     
         66 . The sensor of  claim 1 , further comprising a plasma separation membrane for separating red and white blood cells from plasma. 
     
     
         67 . The sensor of  claim 1 , wherein each one of the photodiodes in the secondary arrays of photodiodes is covered to prevent ingress of light by a metal layer applied directly to the semiconductor substrate. 
     
     
         68 . The sensor of  claim 1 , wherein the printed circuit board comprises an opaque coating across the face of the printed circuit board except in a region of the semiconductor substrate. 
     
     
         69 . The sensor of  claim 1 , wherein the plurality of microfluidic detection chambers comprises a first subset of microfluidic detection chambers and a second subset of microfluidic detection chambers, and the microfluidic substrate comprises a junction configured to distribute a sample between the first subset of microfluidic detection chambers and the second subset of microfluidic detection chambers. 
     
     
         70 . The sensor of  claim 1 , further comprising a controller configured to obtain the primary charge count and the secondary charge count and to calculate the adjusted charge count, wherein optionally the adjusted charge count is calculated by subtracting the secondary charge count from the primary charge count and/or wherein the adjusted charge count is calculated independently for each sensing channel. 
     
     
         71 . The sensor of claim  71 , wherein the controller is configured to compare the adjusted charge count for the first subset of microfluidic detection chambers with the adjusted count for the second subset of microfluidic detection chambers. 
     
     
         72 . A sensor assembly comprising:
 a sensor card comprising the sensor of  claim 1 ; and   a sensor card receiver.   
     
     
         73 . A method for sensing photons in liquids, the method comprising
 providing a sensor that comprises:
 a microfluidic substrate, wherein the microfluidic substrate is non-transparent such as to prevent photons from passing through the microfluidic substrate, the microfluidic substrate comprising a planar face and a plurality of microfluidic detection chambers each configured to receive a volume of liquid of less than 5 micro litres, wherein each microfluidic detection chamber comprises a transparent aperture located in the planar face; 
 a semiconductor substrate comprising a plurality of single photon avalanche photodiodes facing the planar face of the microfluidic substrate and arranged in a plurality of primary arrays of photodiodes and at least one secondary array of photodiodes, 
 a plurality of sensing channels, wherein each sensing channel of the plurality of sensing channels comprises one of the microfluidic detection chambers and a corresponding one of the primary arrays of photodiodes arranged such that each photodiode in the primary array is aligned with and no more than 1,000 micrometres from its corresponding microfluidic detection chamber so as to receive photons emitted within the corresponding microfluidic detection chamber, wherein a primary charge count derived from the primary array of photodiodes provides a pre-adjusted value of photon count indicative of a total number of photons emitted within the corresponding microfluidic detection chamber; 
 wherein each one of the photodiodes in the secondary array of photodiodes is covered to prevent ingress of light and wherein a secondary charge count derived from the secondary array of photodiodes is indicative of a dark count; 
   wherein the method comprises:   triggering a luminescent reaction to occur in the microfluidic detection chambers;   obtaining, for each sensing channel, the primary charge count;   obtaining, for each sensing channel, the secondary charge count; and   using the secondary charge count to adjust the primary charge count in order to calculate an adjusted charge count.   
     
     
         74 . The method of  claim 73 , further comprising:
 triggering a first luminescent reaction to occur in a first subset of the microfluidic detection chambers;   triggering a second luminescent reaction to occur in a second subset of the microfluidic detection chambers; and/or   wherein the primary charge count is a median charge count for the photodiodes in the primary array and wherein the secondary charge count is a median charge count for the photodiodes in the secondary array.